More vent holes in the case Low down seems to work and insuring HD spin down. or run in a more eco mode.
Due to the Pi and if yo urun raid its in software you not going to lose preformance but not running drives in “preformace mode” and this in its self will drop the heat out put from them and help cool the over all system.
But number one is air flow to pull the heat out, so best is to have opening both ends of case and fans to pull / push the air through. which you can achive 2 ways
- better fans with existing vents which can pull more air though the restricted space
- create more vents for better air flow with existing fans
Doing both will get best results.
Remeber hot air rises an the hottest part of the set up is the CPU, so idealy you want air flow from top to bottom to aid the fans and I put hold in the side of the case in the bottom 1/4 (2 inches) so air flow in on to the pi board and then drawn up through the disk to exit out the top.
even with top fan off the natural air flow keeps CPU below 45 degrees unless I am really hammering it. once I am hammering it and the fan kicks in it still stays <70.
Pi is designed to run warm and disk as long as they are <50 should be ok, though I like mine at idle to be <40 and pi cpu <50.